The invention relates to a fluid friction clutch for controlling vehicle cooling fan motor drives and the like.
In known fluid friction clutches such as described in commonly assigned U.S. Pat. No. 4,505,367, a bimetallic control element is clamped radially over the cover and, with both its ends, which have corresponding recesses, is clamped under projections of ribs at the cover which are directed toward the inside and are used for the elimination of heat. The bimetallic element which thus is flexibly clamped on both sides, at the front side of the cover, is located in the coupling center or, in constructions having a central screw bolt (DE-PS No. 31 49 105 - D 6325), off-center, rests against an actuating pin which tightly penetrates the cover and, on the inside, presses on a pivoted lever which serves as a valve. Depending on the position of the valve it more or less exposes an opening provided in the partition between the working chamber and the storage chamber. In these cases the arrangement is such that, at higher temperatures, at which the connecting of the clutch is desired which as a rule is assigned to the cooling fan of a motor vehicle radiator, the bimetallic element bends toward the outside away from the cover, so that, as a result, the pin releases the valve lever and this valve lever exposes the valve opening. The clutch fluid will then move from the storage space into the working space, and the clutch housing at which the fan blades are mounted, for example, on the outside, the fan blades are mounted, is taken along by the driven clutch disk by means of the fluid friction.
In order to avoid, in the case of such a flexible mounting, that the adjusted positions of the bimetallic element changes during the operation and that, as result, the connecting or engaging point of the clutch also changes, the two ends of the bimetallic element are secured in their position by means of a silicone stopper applied at the fastening point. However, this type of fastening is not sufficient in all cases in order to ensure a secure hold of the bimetallic element. This is particularly true when the clutch is mounted directly at the crankshaft. The then occurring shaking and stress may result in damage to the fastening points and thus in a change of position of the bimetallic element which is also connected with an undesirable change of the connecting temperature.
An object of the invention is therefore to develop a fluid friction clutch of the initially mentioned type such that the bimetallic element will be fastened securely also in the case of high stress, but will nevertheless have the required freedom of motion at the point of the actuating pin.
In order to achieve this object, in preferred embodiments of the invention, the bimetallic element is clamped at one side and its free unclamped side or end sits upon the pin for actuating the clutch valve.
The one-sided firm clamping-in of the bimetallic element in the manner of a carrier clamped in on one side ensures the free mobility of the other end which acts upon the actuating pin. The fastening can take place in a sufficiently secure manner and makes a motion relative to the cover impossible. There is no danger of an undesirable detaching of the bimetallic element or of a change of position also in the case of high stress to the clutch.
In certain preferred embodiments the bimetallic element extends transversely over the cover with fastening of one end at two pins located in a radial plane. This arrangement, together with a bimetallic element which extends approximately symmetrically with respect to the clutch center, assures that unbalanced masses are avoided when the clutch is rotated. A simple mounting and a precise alignment of the bimetallic element is provided in certain embodiments where one pin is used as a plug in pin to secure the element position and the other pin is a fastening pin.
In a fluid friction clutch of the initially mentioned type having a central screw bolt which is accessible from the front side of the clutch and, as a result, permits a very simple mounting of the clutch, particularly also at the crankshaft, a radial arrangement of the bimetallic element can no longer take place. Especially preferred embodiments provide a very simple solution for this purpose utilizing a V-shaped bimetallic element which also, while largely avoiding occurring imbalances, permits the use of a bimetal element which is clamped in on one side. In especially preferred embodiments the actuating pin is located in a radial plan of the clutch, thus permitting the arranging of the actuating pin at the same point as in the radial arrangement of the bimetallic element. It is therefore not necessary to change the other clutch components, despite the construction with the central screw bolt, with respect to the actuating pin arrangement and the valve lever. In preferred embodiments there is also provided in adjusting threaded correction of the actuating pin, thus permitting a simple adjusting of the position of the valve assigned to the respective position of the bimetal element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.